Keeping Bargnani, Amir and Davis as your three main frontcourt players is going to get you more of the same that we've seen all year. Davis and Amir trying to cover up for the fact that Bargnani can't defend or rebound, and more losing. I want to win, so I'd keep the players who can defend and do the little things. It would be nice to be able to replace Bargnani with a center who can score, rebound AND defend, but at this point, I'd take a rebounder and defender and hope that Davis develops offensively and leave most of the scoring up to the wings.
There aren't many centers who can do that. Actually the only players I can think of are Bynum, Howard and Kaman, and Howard's offense isn't very good (although his hook has been improving)